As a light source device for generating short wavelength light, such as light with a 193 nm wavelength, a light source device having a seed light generation device which generates seed light (single wavelength pulsed light in an infrared or visibile range) to be optically amplified, a light amplification unit which optically amplifies the seed light generated by the seed light generation device, such as an optical fiber amplifier, and a wavelength conversion unit which converts the wavelength of the light optically amplified by the light amplification unit, into a shorter wavelength, for example, is known (e.g. Patent Document 1).
This light source device is used for constituting a light irradiation device for irradiating light onto an object, along with an irradiation optical system for irradiating the light from this light source device onto the object (e.g. Patent Document 1). This light irradiation device is used for an exposure device for transferring a mask pattern onto a photosensitive object, various optical inspection devices, and a laser treatment device, for example (e.g. Patent Document 1).
The seed light generation device is comprised of a distributed feedback laser diode (DFB-LD) for continuous-wave output, and a pulse modulator which is constituted by an electro-optic modulator, which selectively passes and extracts a part of the continuous-wave output of the DFB-LD (Patent Document 1).
In the case of the above-mentioned light source device, it is known that self phase modulation (SPM), which is a kind of nonlinear optical phenomena, is generated in the light amplification unit, and the spectral width increases in the output of the light amplification unit and output of the wavelength conversion unit (output of the light source device) (e.g. Patent Document 1). Depending on the application, problems are generated due to this increase in spectral width. For example, in the case of using this light source device for an exposure device, chromatic aberration of the projection optical system increases, which deteriorates the image forming characteristic of the projection optical system, and drops the transfer accuracy of the mask pattern. In order to suppress the increase of the spectral width due to self phase modulation, Patent Document 1 proposes two methods. The first method disposes a phase modulator, which performs phase modulation on an appropriate position of an optical path in the above-mentioned light source device, so as to cancel at least a part of the self phase modulation of the light traveling the optical path. The second method superimposes a phase modulation signal, used for performing phase modulation to cancel at least a part of the self phase modulation, on a drive signal to be supplied to DFB-LD for continuous-wave output.